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Minerals of Highway-50, Grenville to Pointe-Au-Chêne, Québec, Canada

Last Updated: 9th Oct 2017

By Phil M. Belley

Minerals of Highway-50, Grenville to Pointe-Au-Chêne, Québec, Canada
Philippe M. Belley1, Michel Picard2, Ralph Rowe2, and Glenn Poirier2

1- Dept. of Earth, Ocean, and Atmospheric Sciences, University of British Columbia, Vancouver, B.C., Canada
2- Canadian Museum of Nature, Research & Collections Division, Mineralogy Section, Aylmer, Quebec Canada

INTRODUCTION


Over 80 km of road construction took place from 2006 to 2012 in order to connect two distant segments of Highway-50 from Buckingham to Lachute, Québec. While a large amount of outcrops were blasted throughout the Highway-50 construction zone, only a few produced mineral specimens of interest. The only noteworthy mineral specimen occurrence discovered west of Pointe-au-Chêne consisted of a clay-filled calcite pocket located 470 m west of montée Laurin in Lochaber township (east of Buckingham), where translucent grey calcite crystals were found. The best specimens are an 8 cm twin, and a 38 mm transparent crystal. The most interesting mineral occurrences were located along a 13 km segment of the highway from Pointe-au-Chêne to Grenville (Fig. 1): Numerous marbles and skarns hosted good specimens of diopside, K-feldspar, plagioclase, wollastonite, graphite, vesuvianite, blue calcite, fluorescent scapolite, etc. While many mineral species occurred as micro-crystals, the present article describes mineral specimens of interest to the collector, which have been collected by the authors between 2006 and 2010.
Figure 1. Highway 50 mineral localities, Pointe-Au-Chêne to Grenville, Québec.


REGIONAL GEOLOGY


The calc-silicate skarns and graphitic marbles exposed during Highway-50 construction all occur in close proximity with marble in the granulite grade Morin terrane of the Central Metasedimentary Belt, Grenville Geological Province (Corriveau 2013). Marble, quartzofeldspathic gneiss (locally garnet or cordierite bearing), and quartzite crop out in the Grenville region. These metasedimentary rocks are intruded by the Morin series of plutonic rocks: syenite, granite, monzonite, gabbro, etc (Philpotts 1976). Large roadcuts expose plutonic rocks in the study area. Evidently, the juxtaposition of intrusive rocks and marble creates favourable conditions for calc-silicate skarn formation. Interestingly, the name of the geological province, “Grenville,” originates from a description (ca. 1863) of paragneisses in this area by Sir William E. Logan (Philpotts 1976), the Geological Survey of Canada’s first director after whom the mineral “weloganite” is named (Sabina et al. 1968).


IDENTIFICATION METHODS


Many species have been visually identified. Denoted in the text are the minerals which have been identified with other methods: X-ray powder diffraction (XRPD) and electron probe microanalysis (EPMA).

1 – CALUMET BLUE CALCITE SKARN


Just west of Whinfield road near Calumet, Grenville-sur-la-Rouge

The first outcrop of interest (Fig. 2) was blasted in 2007, which exposed a wollastonite-rich skarn in calc-silicate rock containing masses of blue and pale green calcite in which good mineral specimens were found. Large blocks (up to 2 m in size) of relatively pure, coarsely-crystalline anhedral wollastonite (to over 30 cm long, Fig. 3) were exposed temporarily.
Figure 2. Marble outcrops at locality #1 seen looking east from the Whinfield Road overpass. Most mineral specimens were recovered from blasting and excavation on the floor of the roadcut. Photo by Julie Bourdeau (2007).
Figure 3. Pale green anhedral wollastonite crystals to over 30 cm in calc-silicate rock at locality #1. Photo by Julie Bourdeau (2007).
Figure 2. Marble outcrops at locality #1 seen looking east from the Whinfield Road overpass. Most mineral specimens were recovered from blasting and excavation on the floor of the roadcut. Photo by Julie Bourdeau (2007).
Figure 3. Pale green anhedral wollastonite crystals to over 30 cm in calc-silicate rock at locality #1. Photo by Julie Bourdeau (2007).
Figure 2. Marble outcrops at locality #1 seen looking east from the Whinfield Road overpass. Most mineral specimens were recovered from blasting and excavation on the floor of the roadcut. Photo by Julie Bourdeau (2007).
Figure 3. Pale green anhedral wollastonite crystals to over 30 cm in calc-silicate rock at locality #1. Photo by Julie Bourdeau (2007).

The largest calcite veins were exposed on the floor of the roadcut, which was later backfilled and paved over. Specimens of euhedral wollastonite occurred in blue and green calcite although only one specimen is a fine example of the species (Fig. 4). Occasionally, wollastonite within the calcite skarn is replaced by a fine-grained mixture of quartz and calcite, or by pectolite (both XRPD confirmed; Fig. 5). Graphite, as idiomorphic crystals to 1 cm, are most commonly associated with the green calcite portion of the skarn, but few good specimens were recovered and were of inferior quality to samples from the Avoca road skarns. Plagioclase crystals (1-3 cm, less commonly up to 8 cm) are common in the blue and green calcite skarns and nearly always have an alteration rind of colourless grossular, sometimes itself covered with an alteration rind of yellowish vesuvianite (both XRPD confirmed; Figs. 6 and 7).
Figure 4. Euhedral wollastonite crystal, 2 cm long, on blue calcite, collected by Michel Picard at locality #1. Canadian Museum of Nature collection.
Figure 5. Pectolite replacing wollastonite crystals to 52 mm long in greenish-blue calcite. Specimen found at locality #1. Canadian Museum of Nature specimen.
Figure 6. Plagioclase crystals up to 23 mm, with alteration rims of grossular (white) and vesuvianite (yellowish) from locality #1. Associate minerals include brassy pyrrhotite, green diopside, and blue calcite. Specimen is 62 mm high. Philippe Belley collection.
Figure 7. Plagioclase (Pl) with alteration rims of grossular (Grs) and vesuvianite (Ves) in blue calcite with associated pyrrhotite. Crystal is 14 mm across. Collected by Michel Picard at locality #1. Canadian Museum of Nature Specimen.
Figure 4. Euhedral wollastonite crystal, 2 cm long, on blue calcite, collected by Michel Picard at locality #1. Canadian Museum of Nature collection.
Figure 5. Pectolite replacing wollastonite crystals to 52 mm long in greenish-blue calcite. Specimen found at locality #1. Canadian Museum of Nature specimen.
Figure 6. Plagioclase crystals up to 23 mm, with alteration rims of grossular (white) and vesuvianite (yellowish) from locality #1. Associate minerals include brassy pyrrhotite, green diopside, and blue calcite. Specimen is 62 mm high. Philippe Belley collection.
Figure 7. Plagioclase (Pl) with alteration rims of grossular (Grs) and vesuvianite (Ves) in blue calcite with associated pyrrhotite. Crystal is 14 mm across. Collected by Michel Picard at locality #1. Canadian Museum of Nature Specimen.
Figure 4. Euhedral wollastonite crystal, 2 cm long, on blue calcite, collected by Michel Picard at locality #1. Canadian Museum of Nature collection.
Figure 5. Pectolite replacing wollastonite crystals to 52 mm long in greenish-blue calcite. Specimen found at locality #1. Canadian Museum of Nature specimen.
Figure 6. Plagioclase crystals up to 23 mm, with alteration rims of grossular (white) and vesuvianite (yellowish) from locality #1. Associate minerals include brassy pyrrhotite, green diopside, and blue calcite. Specimen is 62 mm high. Philippe Belley collection.
Figure 7. Plagioclase (Pl) with alteration rims of grossular (Grs) and vesuvianite (Ves) in blue calcite with associated pyrrhotite. Crystal is 14 mm across. Collected by Michel Picard at locality #1. Canadian Museum of Nature Specimen.

Rarely, plagioclase is completely replaced by grossular and vesuvianite (Fig. 8). In one instance, plagioclase is completely replaced by fine-grained prehnite (XRPD confirmed; Fig. 9). Some parts of green calcite skarn contain abundant reddish-brown vesuvianite averaging 8 mm, and up to 17 mm (Fig. 10). Other minerals found in the calcite veins include pyrrhotite, titanite, purplish zircon, apatite, microcline (XRPD confirmed), etc (see Bourdeau 2009 for a list of less common associate minerals).
A fluorescent-scapolite-bearing diopside-rich calc-silicate rock occurs on the west part of the rock face on the north side of the highway. Scapolite-rich veins (over 2 m long) and zones (over 1 m) fluoresce bright orange-yellow when exposed to longwave ultraviolet light (Fig. 11). While most scapolite is massive and fine-grained, pods of coarser-grained pale yellow scapolite occur in a narrow vertical band on the outcrop. The cores of these pods are commonly altered to “wilsonite” (pink, fine-grained muscovite identified with XRPD; Fig. 12).
Figure 8. Vesuvianite (yellowish) and grossular (white) pseudomorph after plagioclase with blue calcite from locality #1. Specimen is 35 mm wide. Philippe Belley collection.
Figure 9. Prehnite pseudomorph after plagioclase, 21 mm, showing earlier grossular-vesuvianite alteration rims in blue calcite. Collected by Michel Picard at locality #1. Canadian Museum of Nature specimen.
Figure 10. Vesuvianite crystals up to 17 mm on pale green calcite from locality #1. Philippe Belley collection.
Figure 8. Vesuvianite (yellowish) and grossular (white) pseudomorph after plagioclase with blue calcite from locality #1. Specimen is 35 mm wide. Philippe Belley collection.
Figure 9. Prehnite pseudomorph after plagioclase, 21 mm, showing earlier grossular-vesuvianite alteration rims in blue calcite. Collected by Michel Picard at locality #1. Canadian Museum of Nature specimen.
Figure 10. Vesuvianite crystals up to 17 mm on pale green calcite from locality #1. Philippe Belley collection.
Figure 8. Vesuvianite (yellowish) and grossular (white) pseudomorph after plagioclase with blue calcite from locality #1. Specimen is 35 mm wide. Philippe Belley collection.
Figure 9. Prehnite pseudomorph after plagioclase, 21 mm, showing earlier grossular-vesuvianite alteration rims in blue calcite. Collected by Michel Picard at locality #1. Canadian Museum of Nature specimen.
Figure 10. Vesuvianite crystals up to 17 mm on pale green calcite from locality #1. Philippe Belley collection.
Figure 11. Fluorescent scapolite under long wave ultraviolet light, seen on the wall of the north roadcut at locality #1. The fluorescent light is approximately 15 cm (6 inches) long. Photo by Julie Bourdeau (2007).
Figure 12. A pod of scapolite, 4 cm high, in diopside showing alteration to pink fine-grained muscovite (‘wilsonite’). Collected by Michel Picard at locality #1. Canadian Museum of Nature specimen.
Figure 11. Fluorescent scapolite under long wave ultraviolet light, seen on the wall of the north roadcut at locality #1. The fluorescent light is approximately 15 cm (6 inches) long. Photo by Julie Bourdeau (2007).
Figure 12. A pod of scapolite, 4 cm high, in diopside showing alteration to pink fine-grained muscovite (‘wilsonite’). Collected by Michel Picard at locality #1. Canadian Museum of Nature specimen.
Figure 11. Fluorescent scapolite under long wave ultraviolet light, seen on the wall of the north roadcut at locality #1. The fluorescent light is approximately 15 cm (6 inches) long. Photo by Julie Bourdeau (2007).
Figure 12. A pod of scapolite, 4 cm high, in diopside showing alteration to pink fine-grained muscovite (‘wilsonite’). Collected by Michel Picard at locality #1. Canadian Museum of Nature specimen.



2- KILMAR ROAD OCCURRENCE


Roadcut at the intersection of Kilmar and Welden roads, just south of Hwy-50, west of Calumet, Grenville-sur-la-Rouge
This occurrence was blasted to make way for the displaced Welden road, as part of the Highway-50 construction project (Fig. 13). A coarse-grained skarn is now exposed. It is principally composed of off-white calcite (with cleavages up to 20 cm) with dark green clinopyroxene crystals to over 20 cm long, reddish-brown titanite (Fig. 14) up to 3 cm, poorly-formed scapolite to 15 cm, and K-feldspar crystals to 15 cm (XRPD confirmed; only smaller specimens are attractive, i.e., Fig. 15). During early construction, we found a large vug (the calcite having been naturally weathered away) containing sharp clinopyroxene crystals to 20 cm. The largest sample was 2 meters wide with the crystal cavity facing down which prevented specimens from being recovered. However, a large specimen with 15 cm clinopyroxene crystals and a single feldspar crystal was recovered on the same day (Fig. 16). Under the sand at the western tip of the outcrop, on the north side of Welden road, massive graphite occurs abundantly in dark calc-silicate rock and fine-grained marble. A 1 cm graphite layer also occurs between these two lithologies (Fig. 17).
Figure 13. Titanite-bearing clinopyroxene-calcite skarn at locality #2, seen looking NW. The left wall has since been blasted to make way for Welden road. Michel Belley photo (2008).
Figure 14. Reddish brown titanite crystal, 25 mm high, with a poorly formed feldspar crystal from locality #2. Philippe Belley collection.
K-feldspar crystal, 55 mm long, with a re-healed fracture on K-feldspar matrix from locality #2. Philippe Belley collection.
Figure 14. Reddish brown titanite crystal, 25 mm high, with a poorly formed feldspar crystal from locality #2. Philippe Belley collection.
K-feldspar crystal, 55 mm long, with a re-healed fracture on K-feldspar matrix from locality #2. Philippe Belley collection.
Figure 14. Reddish brown titanite crystal, 25 mm high, with a poorly formed feldspar crystal from locality #2. Philippe Belley collection.
K-feldspar crystal, 55 mm long, with a re-healed fracture on K-feldspar matrix from locality #2. Philippe Belley collection.
Figure 16. A large specimen of clinopyroxene (crystals up to 15 cm), with a crystal of feldspar. Collected by Michel and Philippe Belley at locality #2. Canadian Museum of Nature specimen.
Figure 17. A saddle-shaped covering of graphite on marble, which occurred at its contact with a dark calc-silicate rock at locality #2. Specimen measures 6 x 7 x 11 cm. Philippe Belley collection.
Figure 16. A large specimen of clinopyroxene (crystals up to 15 cm), with a crystal of feldspar. Collected by Michel and Philippe Belley at locality #2. Canadian Museum of Nature specimen.
Figure 17. A saddle-shaped covering of graphite on marble, which occurred at its contact with a dark calc-silicate rock at locality #2. Specimen measures 6 x 7 x 11 cm. Philippe Belley collection.
Figure 16. A large specimen of clinopyroxene (crystals up to 15 cm), with a crystal of feldspar. Collected by Michel and Philippe Belley at locality #2. Canadian Museum of Nature specimen.
Figure 17. A saddle-shaped covering of graphite on marble, which occurred at its contact with a dark calc-silicate rock at locality #2. Specimen measures 6 x 7 x 11 cm. Philippe Belley collection.


3- AVOCA ROAD OCCURRENCE


Pointe-au-Chêne
Roadcut “A” on a highway ramp just west of Avoca road;
Roadcut “B” on unnamed road just north of Hwy-50 and west of Avoca road.

Two roadcuts near Avoca road exposed graphite-rich feldspathic rock and marble. A roadcut on the highway ramp (roadcut “A”) contained unusual K-feldspar pseudomorphs after an unknown mineral, presumably analcime, on calcite crystals hosted in a thin vein (Figs. 18, 19). A graphite slickenside in excess of 1.5 meters in size was temporarily exposed near the floor of the roadcut on its eastern corner (Fig. 20). Some of the extracted slickenside samples show exquisite detail (Fig. 21).
Figure 18. Feldspar pseudomorphs after possible analcime with calcite at locality #3A. The crystal-bearing face is roughly 40 cm wide. Photo by Julie Bourdeau (2010).
Figure 19. Feldspar pseudomorph after possible analcime crystals from locality #3A, 24 mm across. Philippe Belley collection.
Figure 20. Graphite slickenside at locality #3A. Photo by Julie Bourdeau (2010).
Figure 21. Graphite slickenside from locality #3A, 12 cm wide. Philippe Belley collection and photo.
Figure 18. Feldspar pseudomorphs after possible analcime with calcite at locality #3A. The crystal-bearing face is roughly 40 cm wide. Photo by Julie Bourdeau (2010).
Figure 19. Feldspar pseudomorph after possible analcime crystals from locality #3A, 24 mm across. Philippe Belley collection.
Figure 20. Graphite slickenside at locality #3A. Photo by Julie Bourdeau (2010).
Figure 21. Graphite slickenside from locality #3A, 12 cm wide. Philippe Belley collection and photo.
Figure 18. Feldspar pseudomorphs after possible analcime with calcite at locality #3A. The crystal-bearing face is roughly 40 cm wide. Photo by Julie Bourdeau (2010).
Figure 19. Feldspar pseudomorph after possible analcime crystals from locality #3A, 24 mm across. Philippe Belley collection.
Figure 20. Graphite slickenside at locality #3A. Photo by Julie Bourdeau (2010).
Figure 21. Graphite slickenside from locality #3A, 12 cm wide. Philippe Belley collection and photo.

Roadcut “B” exposes several rock types: graphitic marble; graphitic quartz-feldspar veins, some containing brown prisms of fluor-uvite (EPMA confirmed) up to 2 cm which rarely have exposed terminations; mica-rich marble, rarely with euhedral phlogopite (Fig. 22); diopside skarn containing euhedral, light purple to brownish purple diopside to over 10 cm wide in coarse-grained, yellowish calcite (Fig. 23). The diopside is very friable, which prevented the recovery of any good samples. Small transparent fragments of diopside have been faceted into stones up to 0.55 ct. The largest graphite crystal found here measures 3 cm across, but its crystal shape is occluded by parallel growth. The largest idiomorphic hexagonal crystals do not exceed 11 mm (Fig. 24). Rosettes and irregular clusters of graphite crystals occur in the marble or at the contact between marble and quartz-feldspar veins (Figs. 25, 26). A significant quantity of well-formed graphite crystals averaging 5 mm were found with pyrrhotite in fine-grained wollastonite (Fig. 27) in blocks used for backfill near the pyrite occurrence (occurrence #4), which most likely originates from Roadcut “B”.
Figure 22. Prismatic phlogopite crystal, approximately 7 cm long, in marble at locality #3B. The specimen could not be recovered. Photo by Julie Bourdeau (2010).
Figure 23. Large crystals of reddish-brown diopside in yellow to white calcite at locality #3B. Photo by Julie Bourdeau (2010).
Figure 22. Prismatic phlogopite crystal, approximately 7 cm long, in marble at locality #3B. The specimen could not be recovered. Photo by Julie Bourdeau (2010).
Figure 23. Large crystals of reddish-brown diopside in yellow to white calcite at locality #3B. Photo by Julie Bourdeau (2010).
Figure 22. Prismatic phlogopite crystal, approximately 7 cm long, in marble at locality #3B. The specimen could not be recovered. Photo by Julie Bourdeau (2010).
Figure 23. Large crystals of reddish-brown diopside in yellow to white calcite at locality #3B. Photo by Julie Bourdeau (2010).
Figure 24. Graphite crystals to 11 mm in marble from locality #3B. Philippe Belley collection.
Figure 25. Irregular clusters of graphite, up to 25 mm, on quartz-feldspar matrix. Calcite was removed with hydrochloric acid. Collected by Michel Picard at locality #3B. Canadian Museum of Nature collection.
Figure 26. Graphite rosette, 12 mm, in pale green calcite in diopside-bearing marble. Collected by Michel Picard at locality #3B. Canadian Museum of Nature collection.
Figure 27. Graphite crystal, 7 mm, on pyrrhotite-bearing wollastonite matrix. Collected by Michel Picard and Philippe Belley from blocks originating from locality #3B. Philippe Belley collection.
Figure 24. Graphite crystals to 11 mm in marble from locality #3B. Philippe Belley collection.
Figure 25. Irregular clusters of graphite, up to 25 mm, on quartz-feldspar matrix. Calcite was removed with hydrochloric acid. Collected by Michel Picard at locality #3B. Canadian Museum of Nature collection.
Figure 26. Graphite rosette, 12 mm, in pale green calcite in diopside-bearing marble. Collected by Michel Picard at locality #3B. Canadian Museum of Nature collection.
Figure 27. Graphite crystal, 7 mm, on pyrrhotite-bearing wollastonite matrix. Collected by Michel Picard and Philippe Belley from blocks originating from locality #3B. Philippe Belley collection.
Figure 24. Graphite crystals to 11 mm in marble from locality #3B. Philippe Belley collection.
Figure 25. Irregular clusters of graphite, up to 25 mm, on quartz-feldspar matrix. Calcite was removed with hydrochloric acid. Collected by Michel Picard at locality #3B. Canadian Museum of Nature collection.
Figure 26. Graphite rosette, 12 mm, in pale green calcite in diopside-bearing marble. Collected by Michel Picard at locality #3B. Canadian Museum of Nature collection.
Figure 27. Graphite crystal, 7 mm, on pyrrhotite-bearing wollastonite matrix. Collected by Michel Picard and Philippe Belley from blocks originating from locality #3B. Philippe Belley collection.




4- PYRITE OCCURRENCE


North side of Hwy-50, east of Moïse road overpass, near Pointe-au-Chêne.

Excavation exposed a short sulphide-bearing calcite vein near the floor of a small roadcut (now backfilled). Small crystals of calcite occurred with iridescent, radial clusters of pyrite (Fig. 28) and small quantities of massive sphalerite.
Figure 28. Highly iridescent, radial pyrite cluster on calcite matrix from locality #4. Note the sphalerite-pyrite vein. The intensity of the colour in the iridescence has noticeably faded over 4 years. Philippe Belley collection (photographed after the find in 2010). Specimen is 44 mm high.


ACKNOWLEDGMENTS


Countless hours of field assistance were provided by Michel Belley, which enabled the recovery of specimens from many zones which were only exposed for short periods of time. We thank Julie Bourdeau for providing some of the locality photographs.

REFERENCES


Bourdeau, J.E. 2009. A mineralogical investigation of a blue-calcite-bearing calc-silicate assemblage from Grenville, QC. B.Sc. Thesis, University of Ottawa.

Corriveau, L. 2013. Structure of the Central Metasedimentary Belt in Québec, Grenville Province; an example from the analysis of high-grade metamorphic terranes. Geological Survey of Canada, bulletin 586 (in French).

Philpotts, A.R. 1976. Southeastern part of Grenville township. Ministère des Ressources Naturelles (Québec), geological report 156.

Sabina, A.P., J.L. Jambor, and A.G. Plant. 1968. Weloganite, a new strontium zirconium carbonate from Montreal Island, Canada. Canadian Mineralogist 9: 468-477.




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Comments

Phil,

What a superb article! Great use of the Mindat tools for writing articles. The high quality video is a significant addition. Great model for locations.

Larry,


Larry Maltby
9th Oct 2017 5:34pm
Hi Larry,

Thanks, glad you like it!

Regards,

Phil

Phil M. Belley
9th Oct 2017 6:20pm

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